The present invention relates generally to tube-launched missiles and more particularly to a system for establishing and maintaining a desired azimuthal alignment of the missile within its launch tube while permitting translation of the missile on its support assembly under shock loads.
In a copending patent application by R. D. Gassler entitled "Missile Longitudinal Support Assembly", and assigned Ser. No. 762,888, there is disclosed an improved longitudinal support assembly for a tube launched missile. This missile support assembly provides axial support to the missile while permitting a certain amount of translation of the missile within its launching tube, also called a canister or silo, under seismic shock conditions. This is a highly desireable feature. The support assembly basically comprises a plurality of axial support rods positioned between a pair of gimbaled rings, the top ring being attached to the skirt of the missile and the bottom ring being attached to the air elevator for the missile.
During on-loading of the missile and the attached support assembly into the launching tube, it has been observed that the missile has a tendency to rotate, causing a misalignment of the umbilical plug thereon with respect to the cutout for the plug in the wall of the launching tube or canister. The exact cause of this rotational movement, often called either clocking or rifling, is not known with certainty, but is probably due to any one or a combination of cable twist, center of gravity offset, canister-missile geometry, pad shape, or launch seal compression. Each of these possible causes of rotational movement of the missile is discussed briefly in the following paragraphs.
the cable used to lower a large missile into its launching tube, for example, is often a twisted cable. The missile is first freely suspended just above the tube to permit missile rotation and to eliminate any cable twist. A relaxed condition, i.e. no cable torque, is established before the missile is inserted into the launching tube. As the missile is on-loaded, the vertical force or tension in the cable changes due to the missile weight being taken up by the launch pad friction. This causes a winding or unwinding of the cable, depending on the way the cable strands are wound, and brings about a torque from the cable which although slight, may be sufficient to clock the missile during its further insertion into the tube. A cross-wound cable would tend to act in a similar manner, although the resulting torque would be much less for this type of cable.
In some instances, the missile center of gravity may be offset radially from the theoretical missile center line. This offset may cause the missile to align to a lower potential energy state with resultant clocking of the missile.
The geometry and tolerances of the launching tube and missile can also bring about clocking during on-loading. Neither the missile nor the launching tube is perfectly round, or straight. The pressure exerted on the pads often placed between the missile and the launching tube wall will tend to seek a lower state of potential energy or total pad pressure. Therefore, the missile may rotate to minimize this potential energy. These geometrical differences can be within normal fabrication tolerances and yet have an appreciable effect on azimuth location or clocking.
The shape of each pad may be such that it offsets in a particular direction upon compression. While the pad rows are sometimes installed with this pad offset tendency aligned oppositely in alternate rows, no pad row is compressed an equal amount because of missile and launch tube geometrical irregularities, and this opposite offset tendency of alternate rows is never completely balanced. This may also cause the missile to clock within the launch tube during on-loading.
Several concepts have been proposed either to correct for misalignment after the missile has clocked during its on-loading, or to prevent its clocking during its on-loading. In one concept, the missile is loaded into the launch tube using an emplacer which holds the missile in the correct azimuth position until the first pad row is inserted into the canister. At this point, the air elevator is used to lower the missile. The missile is allowed to clock but is corrected by each set of air elevator stops. The air elevator stops engage guide rails mounted on an alignment cylinder attached to the missile support assembly. The bottom set of stops guide the missile into the final azimuth position. This method has the disadvantage of high loads on the guide rails and air elevator stops.
Another on-loading concept involves the use of steerable wheels mounted on the missile support assembly and bearing against the inner wall of the launching tube. Azimuth alignment is accomplished by steering the wheels as the missile is lowered into the launching tube. The wheels apply a force on the inner wall of the launch tube to cause the missile to rotate back to the desired azimuth location. This concept requires apparatus for remotely controlling the operation of the steering of the wheels, resulting in added complexity, cost and decreasing the reliability of the system.
In U.S. Pat. No. 3,088,374 issued to J. L. Guyant et al on May 7, 1963, there is disclosed an inching and centering system for rotating a missile in order that access doors in the tube will align with similar openings on the missile. This system requires a complex and expensive hydraulic mechanism positioned near the base of the missile.
The use of a track guide, per se, on the internal wall of a launch tube to maintain alignment of a missile therein is known, and a version thereof is disclosed in U.S. Pat. No. 2,998,754 issued to K. J. Bialy on Sept. 5, 1961. A spring loaded ball bearing assembly attached to the fins of a missile cooperates with grooves in the wall of the launching tube. It is stated in this patent that the use of bearings which roll in the guideways reduces the force necessary to launch the missile since there is less friction and inertia than with sliding launching shoes of prior devices.
While such prior art mechanisms have contacting members between a missile and its launching tube to either prevent, or in some instances impart an axial rotation to a missile during its launching, or to reduce frictional forces during launching, and while such mechanisms might prevent rifling of the missile during its insertion in the launching tube, they all have various drawbacks, such as complexity, poor reliability, large physical size, high cost, etc., which make them unsuitable in certain applications. One feature which they all lack is that they do not permit a controlled movement of the missile in all planes after the missile has been loaded in the container. As mentioned earlier with regard to the copending application of R. D. Gassler, it is desireable to provide a missile support which permits a limited amount of axial and radial translation of the missile within the launch tube to protect the missile when it is subjected to seismic forces or shocks caused by earthquakes or nearby nuclear explosions.